This invention relates generally to endoscopes for use in viewing a region within a body cavity. Endoscopes are optical instruments which are well known in the art, and are very useful in permitting the examination of body cavities without the need for extensive surgery. Currently used endoscopes are comprised of many optical lenses mounted in a tube to relay an image from inside a body cavity for viewing by a physician in order to diagnose various diseases or conditions.
A well known optical system currently in use is disclosed and claimed in U.S. Pat. No. 3,449,037 issued to C. J. Koester on June 10, 1969. The Koester patent discloses a two-dimensional optical image transmitting system which employs a fiber optic bundle, or an equivalent assembly, which is disposed in the optical system so as to have its entrance end portion arranged in optical alignment with a first light relaying system and its exit end portion arranged in optical alignment with a similar light relaying system. The fiber optical system was preferably square in cross section. The first relay system included a prism for providing chromatic dispersion for dispersing the various colors of the white light in a linear array. The second relay system included a second chromatic dispersion prism for recombining the dispersed light.
As Koester pointed out in his patent, prior fiber optical system had experienced difficulty in obtaining high quality resolution in the transmitted image due partly to the appearance of dark spots within the transmitted images caused by reduced transmittance or discontinuity in one or more of the elemental image transmission channels of the fiberoptic bundle, and also partly because of the grid-like or chicken wire effect which appeared in the transmitted image because of the spaces between the individual channels. Koester's use of the chromatic dispersion prisms overcame much of those deficiencies.
For an endoscope, the requirement for an overall diameter of the portion that is inserted into the body is severe, the maximum being of the order of 4 mm. Since room must be allocated for fiberoptic illumination and various mounting tubes, the dimeter of the optical elements is on the order of 2.5 mm. In addition, a further requirement of endoscopes is to have the direction of the field of view inclined at an angle of 30 to 60 degrees or more. In order to achieve the required field of view of between 80 and 100 degrees with maximum brightness, the endoscope objective uses what is known as a "retrofocus" optical design. This design makes it difficult to place both the Koester dispersing prism and the required direction of view prism between the distal negative lens component and the positive lens component while still transmitting a bright and wide field of view. This invention is an improvement over the prior art in that I use a single prism which is a combination of the Koester dispersing prism and the conventional direction of view prism, thereby accomplishing the results of both prisms within extraordinarily small dimensions required for the proper use of an endoscope.